Positive secondary-ion emission from Fe-Ni alloys under O⁺₂ bombardment at 45° incidence

Normalized ionization probabilities α+ are reported for binary Fe-Ni alloys under O+2 bombardment at a 45° incidence angle. It is shown that the dependence of α+ on the composition is much smaller than at normal incidence. Photoemission spectroscopy reveals that both nickel and iron remain essentially metallic under oblique-incidence bombardment, whereas almost complete oxidation occurs at normal incidence. This is attributed to our observation that sputter yields under oxygen bombardment increase much faster than cos α-1.